Common surveillance or monitoring camera devices are systems comprising a digital still camera and having the function of continually capturing still images at intervals of a predetermined period of time. The still image data obtained is stored on a recording medium with image capturing time data added thereto. Useful as recording media are hard disks, optical disks, etc. of great capacity which are accessible randomly for storing still image data which is successive with respect to time. The monitoring camera device erases the image data of the oldest image capturing time when the quantity of image data stored approaches the capacity of the recording medium or the recording capacity set on the recording medium, in order to obviate the likelihood of the camera device becoming unable to capture images upon the quantity of still image data stored exceeding the capacity of the recording medium. This enables the camera device to continually capture still images at intervals of a predetermined period of time unless the user performs an ending manipulation.
The monitoring camera device has the same image capturing mechanism as common digital still cameras, and the still image data to be recorded is prepared according to a known data compressing method such as the JPEG method. The still image data obtained by capturing images is stored temporarily in a buffer memory within the camera device, and image capturing time data is added to the image data, which is then recorded on the recording medium successively. The camera device manages the image data with reference to the image capturing time data. The above-mentioned oldest image data is erased also with reference to the image capturing time. However, the data management with reference to the image capturing time data is likely to involve trouble due to the system of daylight saving time.
Daylight saving time is a system wherein timepieces are advanced by a predetermined period of time from the standard time during a specified period of from spring to fall. Daylight saving time is presently adopted by at least seventy countries. In the U.S., for example, the period of daylight saving time starts at 2 a.m. on the first Sunday of April and ends at 2 a.m. on the last Sunday of October, and during this period, timepieces are advanced by one hour. Stated more specifically with reference to FIG. 12, the period of daylight saving time in 2001 AD starts at 2 a.m. on the first Sunday of April, i.e., April 1. Accordingly, the time of day following April 1, 1:59 a.m. is not 2 a.m. but 3 a.m. The period of daylight saving time ends at 2 a.m. on the last Sunday of October, i.e., October 28. The time of day following October 28, 1:59 a.m. is not 2 a.m. but returns to 1 a.m.
Monitoring camera devices comprise a timepiece adapted for daylight saving time and are given image capturing time data by the timepiece. During the period of daylight saving time, the timepiece adapted for this system calculates daylight saving time by adding a predetermined time correction value to the standard time. Such a timepiece needs to have set therein information serving to provide a basis for judging whether the current time is within the period of daylight saving time. Generally provided as this information are conditions for a transition from the standard time to daylight saving time (hereinafter referred to as “DST transition conditions”) which are determined for each year and which comprise the starting time and ending time of the period of daylight saving time. In the case of the U.S. in 2001 AD shown in FIG. 12, determined as the DST transition conditions are “the first Sunday (1st)of April, 2 a.m.” as the starting time of the period of daylight saving time and “the last Sunday (28th) of October, 2 a.m.” as the ending time of the period. The starting time is expressed in the standard time, and the ending time in daylight saving time.
The surveillance or monitoring camera device is intended for surveillance or monitoring, and successively and continually records image data at intervals of a predetermined period of time, so that image capturing time data for giving information as to the image capturing time or times is important. By erasing the oldest data from the recorded image data, the monitoring camera device is capable of continually capturing still images at intervals of a predetermined period of time and recording the images obtained. Accordingly, the image capturing time data needs to be added to the image data in corresponding relation with the image capturing order. No problem will arise if the system of daylight saving time is not adopted. If the image capturing time data according to the standard time is added to the image data, the image capturing order of the image data can be recognized by reference to the image capturing time data. However, in the case where the system of daylight saving time is adopted, problems will arise because when daylight saving time is changed over to the standard time, a situation will occur wherein time reverts.
With reference to the case of the U.S. shown in FIG. 12 as an example, at the current time of October 28, 2 a.m. in daylight saving time, the time of day output by timepieces returns to the standard time from daylight saving time. The time of day in the standard time is then October 28, 1 a.m. Thus the change of summer time to the standard time involves a lap of time zones (after 1 a.m. and before 2 a.m.).
If times lap which are indicated by the items of image capturing time data corresponding respectively to an item of image data and another item of image data which are obtained by the monitoring camera device, it is impossible to recognize the order of image capturing times corresponding to the respective items of image data. This gives rise to the problem that the monitoring camera device is unable to continue to capture and record images by erasing the oldest data from the recorded image data.
The present invention provides a monitoring camera device which is adapted to continually and successively capture and record images by recognizing the order of image capturing times corresponding to stored image data and erasing old image data, even if a lap of times occurs due to a changeover from daylight saving time to the standard time, and an image data management method for the monitoring camera device.